(function (doc, win, undefined) {
  var docEl = doc.documentElement,
  resizeEvt = 'orientationchange' in win? 'orientationchange' : 'resize',
  recalc = function () {
  var clientWidth = docEl.clientWidth;
  if (clientWidth === undefined) return;
  docEl.style.fontSize = 100 * (clientWidth / 750) + 'px';
  };
  if (doc.addEventListener === undefined) return;
  win.addEventListener(resizeEvt, recalc, false);
  doc.addEventListener('DOMContentLoaded', recalc, false)
})(document, window);